[2026-03 LWG Motion 29] P3980R1 Task’s Allocator Use

source/exec.tex

@@ -7331,6 +7331,13 @@
   @\exposid{state}@<Rcvr> connect(Rcvr&& recv) &&;
 \end{itemdecl}
 \begin{itemdescr}
+\pnum
+\mandates
+At least one of the expressions
+\tcode{allocator_type(get_allocator(get_env(rcvr)))} and
+\tcode{allocator_type()}
+is well-formed.
+
 \pnum
 \expects
 \tcode{bool(\exposid{handle})} is \tcode{true}.
@@ -7458,9 +7465,6 @@
   template<class T, class Environment>
   class task<T, Environment>::promise_type {
   public:
-    template<class... Args>
-      promise_type(const Args&... args);
-
     task get_return_object() noexcept;
 
     static constexpr suspend_always @\libmember{initial_suspend}{task::promise_type}@() noexcept { return {}; }
@@ -7483,15 +7487,17 @@
 
     @\unspec@ get_env() const noexcept;
 
-    template<class... Args>
-      void* operator new(size_t size, Args&&... args);
+    void* operator new(size_t size);
+    template<class Alloc, class... Args>
+      void* operator new(size_t size, allocator_arg_t, Alloc alloc, Args&&...);
+    template<class This, class Alloc, class... Args>
+      void* operator new(size_t size, const This&, allocator_arg_t, Alloc alloc, Args&&...);
 
     void operator delete(void* pointer, size_t size) noexcept;
 
   private:
     using @\exposidnc{error-variant}@ = @\seebelownc@;    // \expos
 
-    allocator_type    @\exposidnc{alloc}@;            // \expos
     stop_source_type  @\exposidnc{source}@;           // \expos
     stop_token_type   @\exposidnc{token}@;            // \expos
     optional<T>       @\exposidnc{result}@;           // \expos; present only if \tcode{is_void_v<T>} is \tcode{false}
@@ -7519,25 +7525,6 @@
 \tcode{execution::completion_signatures} denoted by
 \tcode{error_types}.
 
-\indexlibraryctor{task::promise_type}%
-\begin{itemdecl}
-template<class... Args>
-  promise_type(const Args&... args);
-\end{itemdecl}
-\begin{itemdescr}
-\pnum
-\mandates
-The first parameter of type \tcode{allocator_arg_t} (if any) is not
-the last parameter.
-
-\pnum
-\effects
-If \tcode{Args} contains an element of type \tcode{allocator_arg_t}
-then \exposid{alloc} is initialized with the corresponding next
-element of \tcode{args}.
-Otherwise, \exposid{alloc} is initialized with \tcode{allocator_type()}.
-\end{itemdescr}
-
 \indexlibrarymember{get_return_object}{task::promise_type}%
 \begin{itemdecl}
 task get_return_object() noexcept;
@@ -7679,10 +7666,19 @@
 \returns
 An object \tcode{env} such that queries are forwarded as follows:
 \begin{itemize}
-\item \tcode{env.query(get_scheduler)} returns \tcode{scheduler_type(\exposid{SCHED}(*this))}.
-\item \tcode{env.query(get_allocator)} returns \exposid{alloc}.
-\item \tcode{env.query(get_stop_token)} returns \exposid{token}.
-\item For any other query \tcode{q} and arguments \tcode{a...} a
+\item
+\tcode{env.query(get_scheduler)} returns
+\tcode{scheduler_type(\exposid{SCHED}(*this))}.
+\item
+\tcode{env.query(get_allocator)} returns
+\tcode{allocator_type(get_allocator(get_env(\exposid{RCVR}(*this))\brk{}))}
+if this expression is well-formed and
+\tcode{allocator_type()} otherwise.
+\item
+\tcode{env.query(get_stop_token)}
+returns \exposid{token}.
+\item
+For any other query \tcode{q} and arguments \tcode{a...} a
 call to \tcode{env.query(q, a...)} returns
 \tcode{\exposid{STATE}(*this)}. \tcode{environment.query(q, a...)} if this expression
 is well-formed and \tcode{forwarding_query(q)} is well-formed and is \tcode{true}.
@@ -7692,28 +7688,33 @@
 
 \indexlibrarymember{operator new}{task::promise_type}%
 \begin{itemdecl}
-template<class... Args>
-  void* operator new(size_t size, const Args&... args);
+void* operator new(size_t size);
 \end{itemdecl}
+
 \begin{itemdescr}
 \pnum
-If there is no parameter with type \tcode{allocator_arg_t} then let
-\tcode{alloc} be \tcode{allocator_type()}.
-Otherwise, let \tcode{arg_next} be the parameter
-following the first \tcode{allocator_arg_t} parameter,
-and let \tcode{alloc} be \tcode{allocator_type(arg_next)}.
-Let \tcode{PAlloc} be \tcode{allocator_traits<allocator_type>::template
-rebind_alloc<U>}, where \tcode{U} is an unspecified type
+\effects
+Equivalent to:
+\tcode{return operator new(size, allocator_arg, allocator_type());}
+\end{itemdescr}
+
+\indexlibrarymember{operator new}{task::promise_type}%
+\begin{itemdecl}
+template<class Alloc, class... Args>
+  void* operator new(size_t size, allocator_arg_t, Alloc alloc, Args&&...);
+template<class This, class Alloc, class... Args>
+  void* operator new(size_t size, const This&, allocator_arg_t, Alloc alloc, Args&&...);
+\end{itemdecl}
+\begin{itemdescr}
+\pnum
+Let \tcode{PAlloc} be
+\tcode{allocator_traits<Alloc>::template rebind_alloc<U>},
+where \tcode{U} is an unspecified type
 whose size and alignment are both \mname{STDCPP_DEFAULT_NEW_ALIGNMENT}.
 
 \pnum
 \mandates
-\begin{itemize}
-\item The first parameter of type \tcode{allocator_arg_t} (if any) is not the last parameter.
-\item \tcode{allocator_type(arg_next)} is a valid expression if there is a parameter
-of type \tcode{allocator_arg_t}.
-\item \tcode{allocator_traits<PAlloc>::pointer} is a pointer type.
-\end{itemize}
+\tcode{allocator_traits<PAlloc>::pointer} is a pointer type.
 
 \pnum
 \effects